This invention relates to telephone cable repair apparatus and more particularly to such apparatus for locating high resistance faults in the conductors of telephone cables.
The problem of high resistance faults or leaks in telephone cables extending between a central office and its subscriber stations is well-known and may arise as the result of a number of causes, both natural and manmade. Damage to the cable and conductor insulation as the result, for example, of temperature extremes, rodent attack, maintenance negligence, and the like, can permit moisture seepage to establish a high resistance leak between a tip and ring conductor. Whatever the cause, the leaks must be promptly repaired to ensure continuous subscriber service. However, before the leak or fault can be repaired it must first be found and this has frequently presented the major maintenance problem.
One well-known method of pinpointing resistive faults has been the application of a breakdown voltage to the faulty line. The line is first disconnected at the central office and at the subscriber station. Test circuitry is then connected to the tip and ring conductor pair, which circuitry applies a breakdown voltage of the order of 600 volts to the now floating line. As a result the line is caused to breakdown at the fault, thereby creating an arc discharge. The discharge burns away the conductor insulation, typically pulp, and welds the two conductors with molten copper. Once the short circuit between the two conductors is created, a tone signal is applied to the line and is traced to the fault with an exploring coil.
Although a relatively simple procedure, the process of breaking down a faulty line itself has a number of drawbacks. Whether or not a positive weld between the two conductors has been formed is almost impossible to determine. Thus, if the weld was imperfectly formed and is broken before the fault is located, the exploring coil may be passed beyond the point of the fault. The breakdown method also presents a safety hazard to maintenance personnel and to office equipment. Any inadvertent contact with the line or connection to office equipment during the application of the high breakdown voltage could result in injury or equipment damage. The application of a relatively high voltage for unnecessarily long durations to a line having a fault at one point may also cause a breakdown at a second point where an incipient fault exists. Sustained arc durations at the fault can yield unnecessary extensive proximity conductor damage from burning insulation.
It is accordingly one object of this invention to ensure a weld during the operation of breakdown test apparatus in the location of faults in telephone cables.
Another object of this invention is the reduction of risk of injury and equipment damage during the application of a high voltage during the breakdown testing of faulty telephone cables.
It is also an object of this invention to reduce the probability of fire damage to proximity conductors at the fault.
Still another object of this invention is to provide a new and novel test apparatus for locating faults in telephone subscriber lines.